128 



ZOO! 



power (< il] being only equal to lo. this must be multiplied 

 l>y a foivr rqual to 20 to give the Mine product, 200. Finally, 

 by placing the former still nearer to the j)oint of support at </. 

 a force must he given, hut equal to ]oo. lor it- arm of 

 the lever will no longer be more than 2, and 2 X 100 = 2oo. 



Q O 



Fig. 74. 



The disposition of the levers has as much influent > 

 the rapidity of the movements produced, as over their force ; 

 and if by employing a power comparatively feeble we may 

 thus overcome a much stronger resistance, we may also, by 

 employing amoving force having a certain quickness, obtain, 

 by means of these instruments, a movement slower or more 

 rapid. 



Thus let us suppose 



that the power (p) acts v < r ' 



on the lever (a r) so as 

 to cause it to pass to the 

 point of insertion c, a 

 space of 5 in a second, it 

 will displace at the same 

 time the extremity (f) of 

 the lever, and will cause 

 it to arrive at b with a 

 quickness equal to 25, Fig. 75. 



for the distance passed 

 through in equal times by this point will be five times 

 greater than that passed through by the point </. With 

 a force equal in rapidity to 5 we produce, by applying it to the 

 point c, the same result as if we applied to the point / a force 

 having a quickness equal to 25. But all that is gained in 

 rapidity is lost in power or force; for it is chiefly by extend- 

 ing the arm of the lever of resistance to a length dispro- 

 portionate to that of the force, that we obtain these results. 



Now, in the animal economy almost all the levers are so 



